In this known cooling system, a tank penetrated by a forward flow pipe is used for separating the air and fuel gas from the coolant. By means of a relief valve in a valve unit, which is arranged in an elastically supported manner against a closure of a filler neck of the tank, the separated gasses are fed to a compensation, storage and air blocking tank which is acted upon atmospherically. In addition to a coolant reserve, this compensation tank contains an expansion volume which consists of a gas cushion under a defined excess pressure.
With respect to compensation tanks which are formed essentially of rigid walls, for compensation of thermally caused coolant volume changes, elastic connection hoses between the internal-combustion engine and the radiator can be used as additional compensating devices. This is known per se, for example, from U.S. Pat. No. 3,208,438.
Compensation tanks with devices which are elastically flexible at least in certain areas are known from U.S. Pat. No. 3,238,932 and German Patent Document DD-PS 136280.
In each of the systems described in these documents, the necessary pressure buildup in a respective cooling system takes place by compressing a buffer air/gas volume, preferably in the compensation tank. A disadvantage, in this case, is that a relatively large expansion volume is needed in order to be able to absorb the volume increase of the coolant under extreme temperature conditions, such as, for example, reheating of a hot-parked internal-combustion engine, in order to prevent a possible coolant ejection or loss. Further, since the pressure buildup is significantly determined by the volume distribution between the coolant reserve and the buffer gas/air volume in the compensation tank, and when taking into account leakage and evaporation losses, a minimum charging level in the compensation tank is required. The requirement for a large buffer air/gas volume and a sufficient minimum reserve of coolant results in a relatively large compensation tank which, because of its space requirement, is difficult to place in the engine compartment and may cause unfavorable pipe arrangements.
One object of the present invention is to improve a cooling system of the above-mentioned type such that the pressure required in the cooling system for avoiding both premature boiling and pump cavitation is achieved without a prestressed buffer air/gas volume.
This object is achieved by the present invention, which provides the advantage of a combination of compressive stress mechanically generated in the coolant with a forward flow system pressure control. In this case, the gradual shutting-off or release of pressure is achieved into a "pressureless" coolant reserve acted upon by atmosphere. This results in an advantageously small charging, venting and pressure control arrangement which is preferably arranged in the coolant system forward flow from the internal-combustion engine to the radiator.
Advantageous further features of the invention are also described. The detachable arrangement of the valve unit is formed by the relief and vent and return flow valve. Forming the detachable arrangement in the valve connection piece of the forward flow pipe permits a rapid cold charging of the whole cooling system with rapid and reliable venting. The arrangement of the valve unit in the valve connection piece by means of an elastic support against an insert detachably arranged in the filler neck, in conjunction with the pressureless coolant reserve in an operationally warm cooling system, makes opening of the reserve chamber possible without a loss of pressure in the cooling system. Checking of the cooling reserve and optionally of the warm charging is permitted without any risk for the checking person as a result of coolant ejection.
A vent and return flow valve, which connects the compensation chamber with the reserve chamber, and a vent and return flow valve, which connects the forward flow pipe of the cooling system with the reserve chamber, are designed as thermostatic valves. Starting from a defined operating temperature, these thermostatic valves prevent a gas and coolant exchange and thus advantageously contribute to safe opening of the coolant reserve chamber.
The insert described above is detachably arranged in the filler neck and as an abutment for a spring which holds the valve unit in a closed position with respect to the relief valve. The insert is preferably constructed in a pot-shape with a control opening arranged in the bottom for checking the warm charge level. Finally, the displaceable boundary of the compensation chamber is a displacement piston which is arranged by way of roller bellows in a coolant-tight manner and is acted upon by a prestressed pressure spring. The prestressing of the pressure spring may be selected such that, until a predetermined level for reaching the pressure generated by the thermally caused volume change of the coolant in the coolant system is reached, a correspondingly slight displacement of the displacement piston will take place.